Relax register constraints for LMathSqrt.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index 1230cb32e78d8055a2d2abc5915dd78d40f01e5d..5d72524cfe14f368dfefa8d67678c2a8cc5c3ea7 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -3725,9 +3725,14 @@ void LCodeGen::DoMathRound(LMathRound* instr) {
 
 
 void LCodeGen::DoMathSqrt(LMathSqrt* instr) {
-  XMMRegister input_reg = ToDoubleRegister(instr->value());
-  ASSERT(ToDoubleRegister(instr->result()).is(input_reg));
-  __ sqrtsd(input_reg, input_reg);
+  XMMRegister output = ToDoubleRegister(instr->result());
+  if (instr->value()->IsDoubleRegister()) {
+    XMMRegister input = ToDoubleRegister(instr->value());
+    __ sqrtsd(output, input);
+  } else {
+    Operand input = ToOperand(instr->value());
+    __ sqrtsd(output, input);
+  }
 }